Ultra-High Sensitive Fiber Optic Hydrogen Sensor in Air

A compact fiber optic hydrogen sensing system employing self-referenced configuration and controllable light heating technologies, is proposed and experimentally demonstrated with ultra-high sensitivity and wide dynamic range of hydrogen concentration detection. This sensing probe, consisting of nano WO3-Pd2Pt-Pt composite films and single mode fiber inscribed with two Bragg gratings, is principally based on the gasochromic effect of sensitive films. Signal-to-noise ratio of this system can be significantly enhanced with peak intensity of high reflective fiber Bragg grating (I-1, FBG1 written in flat wavelength range of light source) and background intensity (I-2, at a spectral distance of 1nm on the red side of FBG1) as reference intensity and sensing intensity respectively. A 980 nm laser and proportion integration differentiation (PID) controller were employed to ensure the hydrogen sensitive film working at an optimized temperature of 80 degrees C. Hydrogen concentration detection from 0.5 to 12000 ppm in air was achieved by utilizing this sensing system. Experimental results demonstrate the resolution of this hydrogen sensing system can reach 0.2 ppm within range of 1 to 1000 ppm hydrogen exposure. Moreover, this sensor can present a quick response time of less than one second towards 4000 ppm hydrogen in air. Furthermore, the stability of this sensor can be greatly enhanced with controllable optical heating system. The approach proposed in this work can greatly improve the performance of hydrogen sensor, which is very beneficial to its potential application in hydrogen-related facilities.